Stationary-wave measurement of λ
Speaker facing a reflector; microphone moved between them; signal swings max ↔ min. Adjacent maxima are λ/2 apart, so λ = 2d for neighbouring maxima. The mic senses pressure — its maxima sit at displacement nodes. Then v = fλ, compare with 340 m s⁻¹.
What this actually means
Point a speaker at a reflector and the reflected wave overlaps the incident one, forming a stationary wave. Slide a microphone along the line and its signal swings between maxima and minima.
Adjacent maxima are λ/2 apart, so the spacing d between neighbouring maxima gives λ = 2d. Measure across several intervals and divide by the number of INTERVALS: A₁ to A₅ spans four half-wavelengths, not five.
The mic responds to pressure, and pressure varies most where displacement is zero. So the mic's maxima sit at displacement nodes, a reveal examiners consider a discriminator.
Finish with v = fλ and compare against roughly 340 m s⁻¹ for sound in air.
Treating adjacent maxima as λ apart (they are λ/2), or dividing by the count of maxima instead of intervals.
Prove it — watch it be true
- Drag the mic along the rig and drop a flag at each signal maximum
- Read the flag spacing d: the rig confirms λ = 2d
- Open the mic-senses-pressure reveal: your flags sit at displacement nodes
- Compute v = fλ and compare with 340 m s⁻¹